In fuel cells, a fuel and an oxidant are supplied to two electrically-connected electrodes to electrochemically oxidize the fuel, thereby converting chemical energy directly to electrical energy. Unlike thermal power generation, fuel cells are not limited by the Carnot cycle; therefore, they show high energy conversion efficiency. A fuel cell generally comprises a stack of fuel cells, each having an electrolyte layer sandwiched by a pair of electrodes as the basic structure, i.e., a membrane-electrode assembly as the basic structure.
Electrodes provided on both surfaces of an electrolyte membrane generally comprise an electroconductive material and an electrolyte resin (ionomer), the electroconductive material carrying a catalyst. An electrode can be attached to an electrolyte membrane by the following methods, for example: (1) a method of applying an electrode ink to a surface of an electrolyte membrane and drying the same, the ink comprising a catalyst-carrying electroconductive material and an electrolyte resin; and (2) a method of transferring an electrode to an electrolyte membrane by hot pressing, the electrode comprising a catalyst-carrying electroconductive material and an electrolyte resin.
Concrete examples of the above method (2) include those disclosed Patent Literatures 1 to 3.
For example, the method disclosed in Patent Literature 1 is a method for producing a membrane electrode assembly, comprising a step of transferring a catalyst electrode to at least one surface of an electrolyte membrane, the catalyst electrode comprising carbon nanotubes and an ionomer and being formed on a substrate.